Mould, for the purpose of this exercise, is defined as a coating or discolouration caused by various fungi that develop in a damp atmosphere on food, fabrics and walls. Mould, or fungi, has existed on earth since life first began, and results in the natural decomposition of organic materials.

Mould has many similar characteristics to mildew, but they are different types of fungi and are often different in colour and texture. They can sometimes be difficult to tell apart as they both spread out from spores. Mould is often black, green, red or blue in colour, while mildew is usually grey or white. Both mould and mildew thrive in damp environments, so keeping areas dry is the main preventative measure to help eliminate the fungi.

Some types of mould can be a health risk for some people. Reaction to mould is highly variable and is dependent upon the type of mould and the amount. It is clear that some people are allergic to mould. Further, some populations are more susceptible to negative effects from mould exposure. Those who have allergies, asthma or pulmonary conditions may be more susceptible, as well as children and infants. Those with suppressed immune conditions, like HIV/AIDS may risk developing fungal infections in the lungs due to lengthy mould exposure.

Fibreglass duct liners have been incorrectly blamed for contributing to mould growth in high humidity and high temperature conditions. The fact is that fi breglass is inherently resistant to mould growth. The North American Insulation Manufacturers Association (NAIMA) states that “stringent testing in accordance with UL and ASTM standards confi rms that fi breglass duct liners do not support mould growth. In instances where mould growth has been detected on the interior surfaces of the duct system, the cause has been an accumulation of dust and dirt combined with the presence of water. Under these conditions, mould can grow on any interior surface.”

A recent Duke University study links mould growth to dew point conditions rather than the relative humidity. Researchers found that sustained mould growth could occur when wet conditions were produced through condensation, as the air is cooled past its dew point. It is important to note, however, that condensation is not the only source of water in an HVAC system. It can occur as a result of water carryover due to faulty coil design, dirty coils
or failure of the drain pan to operate properly, or improperly operating humidifiers.

Other facts from this same study show that mould growth is not surface specifi c and can be found on any surface of the HVAC system including metal fl ex duct, the fl at surfaces of metal ducts, plastic-lined fl ex duct, caulks and sealants, conditioning coils, metal sound attenuators, mixing box dampers and internal duct liners. It is strongly suggested that removing excess water from supply air will minimize conditions that can result in sustained microbial growth.

NAIMA emphatically states the “fibreglass insulations are inorganic and inert and do not support mould growth. The conditions which promote mould growth – the presence of dust and dirt combined with water – do not normally occur in properly designed, installed, operated and maintained systems. Mould is no more likely to grow on fi breglass than on any other surface in the duct system. Mould grows in the presence of water. By helping to reduce condensation, fibreglass insulated ducts actually help minimize microbial growth. A regular maintenance schedule, along with an efficient fi ltration system, assures protection of both HVAC system components and building occupants. In instances where water is allowed to accumulate in the system, and/or the system is shut down for periods of time, conditions can occur which allow mould growth to occur in the air
handling duct system, whether it is lined or unlined.”

There are many papers and websites to obtain further information on this topic. In its publication, Indoor Air Quality, SMACNA makes several system design and maintenance recommendations to prevent mould growth. These maintenance procedures include inspection, detection and remediation of probable sources of airborne contaminants and water. Also available is an exhaustive guideline document (CCA82) from the Canadian Construction Association titled, Mould Guidelines for the Canadian Construction Industry. This thorough document also outlines building operation and maintenance
procedures for the HVAC system and documents measures for reducing mould growth in HVAC systems. They also introduce a checklist for visually determining the presence of mould in an existing building and provide detailed methods of remediation of HVAC systems that have become contaminated with active mould growth, spores and associated contaminants.

With the increased media coverage of the possible health risks of mould in schools, courthouses, homes and other public and private buildings, and the associated legal issues and insurance claims, mould has become a very hot topic and one that will become even more contentious in the next number of years. ■

Garth Liseth has been involved in the mechanical insulation industry since 1973 and is the past president of TIAC (The Thermal Insulation Association of Canada). Garth is employed by Crossroads C&I Distributors in their Burnaby, BC location.